Examples and processes for the preparation of 2-arylisoxazolin-3-one derivatives are described in Heterocycles, 20(6), pp.1123-1126 (1983), Chemical and pharmaceutical Bulletin, 30(9), pp.3097-3105, Heterocycles, 19(3), pp.515-520, Heterocycles, 19(3), pp.521-524, Journal of the Heterocyclic Chemistry, 17(4), pp.727-731, Chemical and Pharmaceutical Bulletin, 19(7), pp.1389-1394, Japanese Patent Application (OPI) No. 104,274/80 (the term "OPI" as used herein means an "unexamined published application"), etc. However, derivatives where the substituent in the 2-position is an aryl group having a group which is more electron attractive than a chlorine atom are not known. Also, derivatives where a methyl group mono-substituted by a nitrogen or sulfur atom is bound to the 4-position are not known.